The present invention relates to the recording of information using a scanning beam, and more particularly to the registration of image information on a recording medium such as photographic film.
Various systems are well known for recording information on different media. For example, a simple camera records image information on photographic film. In a more sophisticated setting, light beams such as those produced by cathode ray tubes ("CRT") or lasers are scanned line-by-line across photographic film to produce an image. An example of such apparatus can be found in an "image recorder" used to expose film with computer generated images for the production of slides, transparencies, photographs, and the like. An image recorder must be precisely controlled to provide high quality imaging that is consistent on a frame-by-frame basis. Consistency is particularly important for slides that are to be part of a multi-image program using two or more projectors to fade one slide into the next or simultaneously project a plurality of slides that must line up precisely. This requires consistency of both centering and frame-to-frame registration. In cinematographic applications, frame-to-frame misregistration of only a few pixels would result in substantial bounce in the projected image. Precise registration is therefore imperative.
Known image recorders, such as those sold under the trademark "Solitaire" by Management Graphics, Inc. of Minneapolis, Minn., U.S.A., typically include a CRT for producing a beam, a deflection system for scanning the beam across the face of the CRT, a system control and central processor unit ("CPU") for controlling the deflection system, and a camera (i.e., "film transport"). The latter component includes a film transport body, lens, lens mounting assembly, aperture plate, film plane, and film transport mechanism. An image to be recorded is first written on the phosphor of the CRT by deflecting an electron beam in a raster pattern and modulating the intensity of the beam. This process is analogous to the creation of a television picture. Alternately, the image can be written on the CRT using well known time modulation techniques, wherein the beam intensity is constant but the time the beam is kept at each point is varied depending on the exposure required. Time modulation exposure is slower, but generally results in a sharper image.
The resulting pattern (the "object image") on the CRT is optically imaged onto photographic film by the camera, which contains the required optics and mechanism to advance the film to successive frames. A key requirement of the camera is that it hold the film accurately at the film plane so that the CRT image is placed at the proper location on the film. In other words, the object image must be centered, have the proper size, be in focus, and not be rotated with respect to the film path.
In order to provide proper registration (i.e., centering and rotation) of an image on the film, known image recorders typically advance the film within the transport using an expensive, complicated and highly precise mechanism that locks each frame of the film into proper orientation with respect to the transport by placing locating pins into sprocket holes provided in the film. The locating pins must be tediously aligned with respect to the CRT object image prior to the commencement of image recording. To accomplish this, the pins must first be aligned to the aperture and film within the film transport. Then, the transport must be separately aligned to the CRT.
One way to align the transport to the CRT has been to center the transport over the CRT using adjusting screws. The film plane and lens mount are adjusted by means of mechanical shims, and the lens is refocused to achieve the desired image. A test roll of film is exposed on a frame-by-frame basis, with each frame corresponding to different mechanical adjustment settings. A log is kept as to the settings for each frame. After the film is developed, the best settings are determined, and used as a starting point for another iteration of the entire process. It can take many trial and error settings to obtain the required alignment, and the whole process often takes as long as sixteen hours or more. Once the film transport to CRT alignment has been set, rotation is held fixed by the alignment pins in the transport, and image orientation is guaranteed by the tolerances of the mechanical components in the prealigned transport assembly.
A disadvantage of such a manual alignment process, in addition to its complexity and cost, is that the film transport may not be interchanged with another without having to go through most of the alignment process again. Also, the alignment of an image recorder may not survive mechanical shocks, such as being dropped during shipping or jarring occurring during or after the apparatus is unpacked. Still further, known image recorders require an extremely precise gear mechanism in the film transport to prevent the film from tearing when the registration pins are inserted. The associated mechanism for coupling and subsequently decoupling the film with the pins is also complicated and expensive.
It would be advantageous to provide a method and apparatus for registering an image on a recording medium without the need to tediously align the film transport and the beam source (e.g., CRT). It would be further advantageous for such a method and apparatus to provide for image registration without the need for expensive and complex mechanical mechanisms, such as sprocket hole locating pins. Such a system should also enable any film transport module to be interchanged on the film recorder without the need for mechanical realignment.
The present invention provides an apparatus and method having the aforementioned advantages.